Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.72   10.612%   $210.9592   $210.96   $210.95   $211.00  
  Purchase #2 $183.87   9.152%   $200.6978   $200.70   $200.70   $200.70  
  Purchase #3 $168.99   13.331%   $191.5181   $191.52   $191.50   $191.50  
  Purchase #4 $182.74   10.415%   $201.7724   $201.77   $201.75   $201.80  
  Purchase #5 $107.87   10.628%   $119.3344   $119.33   $119.35   $119.30  
  Purchase #6 $187.29   13.387%   $212.3625   $212.36   $212.35   $212.40  
  Purchase #7 $152.39   9.383%   $166.6888   $166.69   $166.70   $166.70  
  7 purchase totals = $1,173.87       $1,303.3332   $1,303.33   $1,303.30   $1,303.40